In the first series of the show audiences learned that synth Anita is actually conscious and called Mia but was hacked and sold with new software.

Speaking on location at a seaside cafe during filming of the second series, Chan said slipping back into the robotic role, in which she stares straight ahead, was rife with challenges.

She said: "I was really appalling the first week, I was like Bambi. You think you'd retain that muscle memory but I was really, really bad.

"Also in my mind I thought it would be easier. It really, really wasn't.

"I nearly fell down the stairs, I just comically stumbled.

"There's a whole flight of steps leading down to the cafe and there was a big shot and it was like, 'If you can just do it without looking down', I was like, 'Oh my God, if I fall, I really will hurt myself, this isn't like the carpeted stairs'. It was three flights of stone stairs!"

Despite the prospective pitfalls, Chan, 33, said she was glad she got to maintain the two sides of her character for the second series.

She said: " A lot of the fun was having that duality and the writers have been really clever in finding a way to let me do it for at least the first bit of season two.

"I found that I really missed Anita, she's the most robotic but she has her own personality and she's great fun to play."

She added: "T here are key moments in the series when you see her make a decision about what she's going to do and the stakes are high.

"As it progresses, things don't go to her plan and she has to respond and you see a steelier side to her. I feel like she might go a bit rogue, which I can't wait for."

Nashville star Sam Palladio joins the cast for the second series, alongside Matrix star Carrie-Anne Moss, and he said he was relieved to play a human.

He said: " The level of concentration is something that I'm watching and admiring. She has to count the steps, think about not blinking too much, the breathing, the physicalities and I'm just trying to get through the scenes and I can be expressive and I can show emotions in human ways.

"It's really fun watching Gemma get the balance between having those more human emotions being Mia and watching Gemma as an actress transform into this other character."

Palladio joins the cast fresh from a run as musician Gunnar Scott in Nashville and has been enjoying the contrasts in the shows.

He said: " It's a fantastic change of pace really.

"To come from a world of country music and big-town America to this really interesting dark British world is a thrill, it really is, and working with Gemma and some of the other cast of the show is very exciting territory and very different for me, which made me all the more excited to be here."